Nazi comes from the German word for National Socialist (Nationalsozialistische). A Nazi is a person who believes in the ideologies and practices of the National Socialist German Workers' Party (Nationalsozialistische Deutsche Arbeiterpartei), abbreviated NSDAP, a racialist (belief that one race is superior to others), totalitarian (government having absolute and centralized control) political party in Germany between 1919 and 1945. It was known as the German Workers' Party (DAP) before the name was changed in 1920.
While Nazism incorporated elements from both left and right-wing politics, the Nazis formed most of their alliances on the right. The Nazis were one of several historical groups that used the term National Socialism to describe themselves, and in the 1920s they became the largest such group.

Among the key elements of Nazism were anti-parliamentarism, Pan-Germanism (a political movement aiming for unity of the German-speaking peoples of Europe), racism, collectivism (any moral, political, or social outlook, that stresses human interdependence and the importance of a collective, rather than the importance of separate individuals), antisemitism (intense dislike for and prejudice against Jewish people), anti-communism, totalitarianism and opposition to economic liberalism and political liberalism, and eugenics (scientific field involving the selective breeding of humans in order to achieve desirable traits in future generations).

Nazi eugenics were Nazi Germany's racially-based social policies that placed the improvement of the race through eugenics at the center of their concerns and targeted those humans they identified as "life unworthy of life" (Lebensunwertes Leben), including but not limited to the criminal, degenerate, dissident, feeble-minded, homosexual, idle, insane, religious, and weak, for elimination from the chain of heredity. More than 400,000 people were sterilized against their will. Adolf Hitler (Führer and Chancellor of Germany unitl 1945) believed the nation had become weak, corrupted by the infusion of degenerate elements into its bloodstream which had to be removed as quickly as possible. He also believed that the strong and the racially pure had to be encouraged to have more children, and the weak and the racially impure had to be neutralized by one means or another.

The NSDAP (Nazi Party) assumed power in 1933 in the aftermath and decline of the Weimar Republic. In response to the instability created by the Great Depression, the Nazis sought a Third Way managed economy that was neither capitalism nor communism. Nazi rule effectively ended on May 7, 1945, V-E Day (Victory in Europe Day), when the Nazis unconditionally surrendered to the Allied Powers, who took over Germany's administration until Germany could form its own democratic government.

The swastika has come to represent the Nazis because of it's use on the Nazi flag. The Nazi flag, created by Hitler, has a red background, and a white circle with a black right-facing swastika in the middle. But the swastika predates the Nazis. The earliest consistent use of swastika motifs on record date back to the Stone Age. The swastika has been used as a religious symbol in many different religions. The word swastika comes from a Sanskrit word (svastika) meaning any lucky or auspicious object, and in particular a mark made on persons and things to denote good luck. Although, because of it's association with the Nazis, public showing of the swastika and other Nazi symbols, in Germany, is illegal, except for scholarly or religious reasons.

2. more recently, it has become a slang term used to described people who are overly concerned about details (in an unhealthy way), and like to correct others on every occasion they get. Especially evident on internet forums, blogs, and youtube